As you can easily imagine, on a table with 10,000 or 100,000 addresses, assuming 10% without a corresponding domain, you may end up waiting for 6,000 or 60,000 seconds before the query completes!
You can easily see this yourself, on a smaller scale, running the following query:
select utl_inaddr.get_host_name('127.0.0.2') from dual
ORA-29257: host 127.0.0.2 unknown
ORA-06512: at "SYS.UTL_INADDR", line 4
ORA-06512: at "SYS.UTL_INADDR", line 35
ORA-06512: at line 1
If you really really need to resolve the host name of an incoming ip address, a typical requirement for a web counter for instance, it could be much more performing to create a materialized view where you cache the result of the call to UTL_INADDR.GET_HOST_NAME (this was another smart suggestion of John).
Last but not least, if you are wondering about how you can get the ip address of a remote user, an Oracle Application Express end user for instance, Oracle comes with function GET_CGI_ENV in package OWA_UTIL, a handy utility that returns many useful values given an input string, where, among others there is 'REMOTE_ADDR' (see the documentation for the list of acceptable cgi variables):
select owa_util.get_cgi_env('REMOTE_ADDR') as ipaddr from dual;However if the db server is behind a firewall or proxy, chances are that the address of the firewall is returned, not the remote ip, but this is another story altogether.
See message translations for ORA-29257 and search additional resources.
ORA-29257: host sconosciuto
ORA-29257: host desconocido
ORA-29257: host desconegut
ORA-29257: hôte inconnu
ORA-29257: Host unbekannt
ORA-29257: κεντρικός υπολογιστής άγνωστος
ORA-29257: vært ukendt
ORA-29257: värddatorn okänd
ORA-29257: verten er ukjent
ORA-29257: pääkone on tuntematon
ORA-29257: A(z) gazda ismeretlen.
ORA-29257: gazda nu este cunoscută
ORA-29257: Host is onbekend.
ORA-29257: host desconhecido
ORA-29257: o host é desconhecido
ORA-29257: хост неизвестен
ORA-29257: neznámý hostitel
ORA-29257: hostiteľ neznámy
ORA-29257: host jest nieznany
ORA-29257: ana bilgisayarı tanınmıyor
ORA-29257: host unknown